<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>hello world</title>
        <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no">
        <style>
            #testEle{
                width: 100%;
                height: 300px;
                border-bottom: 1px solid #ccc;
                margin-bottom: 15px;
            }
        </style>
    </head>
    <body>
        <div class="test">
            <div id="testEle"></div>
        </div>
        <button id="undo">撤销</button>
        <button id="redo">重做</button>
        <button id="getJson">获取json</button>
        <button id="downloadPng">获取透明图片</button>
    </body>
</html>